⛈️How to avoid flash floods in slot canyons

Every summer crowds flock to the Southwestern US to explore the subterranean world of slot canyons. In the middle of the summer, these oases can be significantly colder than the desert surface above. Their magical, dark, fluted chimneys and corridors are ripe for social media posting, but there’s a sinister side to these labyrinths that not everyone is aware of.

canyoneering in a slot canyon
Allen family trip down Blarney Canyon

Read this story for a chilling example of the risk flash floods can be when hiking or canyoneering.

Flash floods are defined as floods that rise and fall rapidly within six hours or even within three hours.

Next to heat-related deaths, floods account for the second-highest number of weather-related deaths in the US. Many (42%) of those deaths occurred in flash floods and some within slot canyons with about 100 flood-related deaths per year.

If we look specifically at canyoneering-related deaths, we have a record of about 27 deaths due to flash floods over the past 30 years. That’s about one person per year dying from flash floods while hiking in slot canyons in the US.

This number isn’t significant compared to traffic deaths, or death due to medical conditions, but knowing that we can almost always prevent meeting an untimely demise in a flash flood in canyon country means we need more education and training on how to predict, avoid, and respond to flash floods while hiking in slot canyons.

It doesn’t take much water either. Six inches of flowing water is plenty to knock you off your feet and carry you over a ledge or drown you.

Where do flash floods happen?

Take a quick look at this map and you’ll see that flash floods happen all over the country. Look a little closer and you’ll notice that there are a few hotspots. One is the Gulf Coast. That’s largely due to tropical storms and hurricanes. You’ll also see a significant hotspot in the desert southwest. This is due to strong Mexican monsoon storms that happen in the summer months. So while flash floods can happen all over, they tend to be more common and dangerous in certain areas.

flash flood map
Flash flood deaths from 1959-2019 in the United States (Analysis of Flood Fatalities in the United States, 1959–2019)

When do flash floods happen?

Flash floods can happen at any time. As the name describes, they happen in a flash. The only real ingredients needed for a flash flood are a topographic feature that will contain water and enough water to fill it. This could be a low spot on a road or a deep slot canyon. Flash floods can happen anytime, but in the desert southwest, they’re most common in the summer months of July through September when the monsoon rains come up from Mexico. These strong storms can hit without much warning and dump huge amounts of water on the desert ground.

These monsoons often hit in the mid-afternoon right after the hottest part of the day for a short window of time and then pass. This timing means you can start the day with clear skies and beautiful weather, but after you’ve committed to a deep slot canyon and have little chance of getting out quickly, the storm can hit at the worst time and leave you stuck.

flash flood from monsoon rains
Monsoon storms can cause destructive and dangerous flash floods. NPS/Emily Ogden

How do flash floods happen?

Why aren’t places that get the most rain like the Pacific Northwest prone to flash flooding while the driest states in the country (Nevada, Utah, Arizona) more prone to flash flooding?

The answer has to do with the terrain and soil surfaces. In the southwest, the land is largely dry and barren. There isn’t much tree cover and many surfaces are sandstone or shallow sandy surfaces over bedrock.

This type of terrain doesn’t absorb water. The water just runs off and down the nearest slope. There’s no vegetation or loamy soil to absorb it or slow it down. This means water from an entire region can move quickly downhill into a narrow streambed and then into a slot canyon. This is the exact process that has formed these incredible slots over thousands of years.

This also means that the rain that falls in an entire drainage can quickly collect into larger and larger tributaries and end up roaring down the canyon many miles away that you happen to be hiking in.

How to predict a flash flood

Flash floods can start even with a very localized rainstorm upstream of where you’re at. This means you need to understand where water drains in relation to your planned canyoneering or hiking route. To do this you need to consult your maps.

My preferred method of mapping out flash flood drainages is with Caltopo.

I made this video showing the steps I take to map out a drainage before a canyoneering or hiking adventure.

How to avoid flash floods

When you’ve mapped out the drainage for your intended route, you need to also consider what your options are when you’re in the canyon. Will you be able to scramble to high ground if you detect a flash flood coming? What terrain traps exist that you need to be wary of? How will you manage your day around these traps?

With your drainage map, you’ll be better able to tell the likelihood of flash flooding for your route if it’s not provided in the beta, but most beta sites will tell you the flash flood risk. Even with beta, you’ll want to carefully review your mapped route for extended slot sections without escapes. These are often the sections of canyons that take longer to navigate so plan on spending more time there. This risk is important to consider in your plans.

If there’s a long section of narrow canyon with high walls, plan to move through it quickly without stopping for lunch or a rest. Plan stops at strategic points that have exit ramps or high ground you can scramble to in case of a flood. Some canyons have little or no accessible high ground so knowing your risk and planning accordingly before going in is key to a safe trip.

These are all considerations to avoid flash floods while in canyons, but perhaps the most important is the weather forecast. If it doesn’t rain in the drainage, you won’t have a flood risk.

For my forecasts, I like to use Windy.com. They have excellent map layering tools that let me see the potential rainfall over an extended period. Radar maps help visualize the drainage of concern to see what the rainfall potential is. You can toggle between different models for a broader perspective on potential risk. Here’s a quick video I made of how I approach forecasting weather.

Most forecasts within a 12-hour period before your outing will be relatively accurate, but the nature of monsoon rain in the desert can be fickle. A thunderburst can drop tons of rain on one side of a drainage and miss the other.

Keep your senses sharp

Despite your best planning, you also need to always be watching the sky and listening. If you see dark clouds roll in, hear thunder, if the wind picks up and the temperature drops, or if you notice the water in the streambed gets muddy and starts to flow faster, these are all signs you should find high ground.

Pay attention and be prepared to act if you notice these red flags.

What if you get caught in a flash flood

So the forecast called for clear skies, but you still find yourself in a thunderstorm. It happens.

The first thing to do is seek high ground. Get up out of the watercourse as quickly as you can. If you find a safe place, be prepared to stay put for several hours or overnight until the water subsides. If it’s raining you’ll likely be wet and cold so be prepared for this with proper shelter, food, and fire building skills.

Here’s an article on what I pack in my emergency kit for just such an occasion.

If you can’t find a safe place, do your best to find a protected location. Get up as high as possible and hide behind boulders or logs or on the inside of a turn if possible. The water coming at you will be forceful and will also likely be loaded with branches, logs, and other debris. If there’s no escape and you’re caught in the flood, take shelter and brace for impact.

Protect your head and neck and do your best to stay afloat if the water starts to carry you. Put on your helmet and wetsuite if you have them and point your feet downstream to help navigate hazards and absorb impact with obstacles. Use your arms to keep yourself afloat.

flash flood floating
The proper floating position is with your feet forward, and eyes down the canyon.

Stay on the lookout for any chance you may have to exit the watercourse. The less time you spend in the water, the better your chance of survival. You likely won’t have much time to think as you get pummeled down the canyon, but if it widens up do your best to get on land. Help get anyone else in your party to safety if you can. You can use a rope or a branch to help them, but most likely you won’t have time to react before they pass your location.

After the flood subsides and you’re in a safe place, be sure to assess your whole group for injury, hypothermia, shock, or other medical conditions and administer proper first aid.


Canyoneering or hiking in slot canyons is an amazing adventure, but it’s also dangerous. Be prepared for flash floods by mapping the drainage and reviewing the forecast to reduce your risk of getting caught in a flash flood and be prepared in case you do get caught. Above all, get out there, have fun, and get back safely.

Leave a Comment

Scroll to Top